1. Field of the Invention
The present invention relates generally to methods employed for successfully fabricating, testing and transporting a minute transducer that includes a liquid filled chamber which has thin membranes forming portions of the chamber""s wall.
2. Description of the Prior Art
U.S. Pat. No. 5,772,575 (xe2x80x9cthe ""575 patentxe2x80x9d) that issued Jun. 30, 1998, on a patent application filed by S. George Lesinski and Armand P. Neukermans describes transducers used for a fully implantable hearing aid system. As disclosed in the ""575 patent, the fully implantable hearing aid system""s transducer cannot exceed 1.2 mm in diameter, and includes a hollow chamber having two (2) walls that are formed by thin, flexible membranes.
The hollow chamber within these implantable transducers must be completely filled with a liquid material while concurrently excluding gas bubbles (except as such bubbles may be deliberately placed within the hollow chamber to provide a special low pass acoustic filter). In general, the presence of even a small bubble inside the hollow chamber may render the transducer ineffective because it prevents efficient liquid displacement transfer from a first thin membrane, i.e. an input membrane, to a second thin membrane, i.e. an output membrane. Because small orifices and complicated shapes are involved in fabricating an implantable transducer that cannot have a diameter greater than 1.2 mm, and because the surface to volume ratio within the hollow chamber is large, extremely small bubbles may be easily trapped within the hollow chamber during filling.
In addition to technical difficulties associated with bubble free filling of implantable transducers as summarized above, the thin membranes combined with the liquid within the transducer""s hollow chamber presents additional technical difficulties while testing the transducers, and while they are being shipped. For example, the United States Food and Drug Administration (xe2x80x9cFDAxe2x80x9d) requires that class III type implantable devices be tested at an elevated temperature to accelerate failure of defective devices. Heating a liquid filled implantable transducer may cause the liquid within the hollow chamber to expand more rapidly than the rest of the transducer. Consequently, heating an implantable transducer that is filled with water surely increases the pressure of liquid within the hollow chamber, and may rupture or plastically deform one or both of the membranes. Similarly, a possibility exists that unprotected implantable transducers may be damaged during shipping if they are exposed to extreme temperatures.
An object of the present invention is to provide methods for filling transducers of a fully implantable hearing aid system with liquid regardless of the liquid""s vapor pressure.
Another object of the present invention is to provide a method that prevents damaging liquid filled transducers of a fully implantable hearing aid system while testing them at elevated temperatures.
Another object of the present invention is to provide methods that prevent damaging liquid filled transducers of a fully implantable hearing aid system while they are being transported.
The transducer of the fully implantable hearing aid system has a body:
1. which surrounds the hollow chamber and includes at least one thin membrane that forms at least a portion of a wall of the hollow chamber; and
2. at least one passage having:
a. an exit that couples the passage to the hollow chamber; and
b. an entrance that is located distal from the hollow chamber for communicating via the passage with the hollow chamber from outside the implantable transducer,
Bubble free filling of the hollow chamber with a high vapor pressure liquid is effected by first establishing a seal around the entrance of the passage. Then, while protecting the thin membrane from damage, evacuating the hollow chamber through the passage by applying vacuum to the entrance thereof. After the hollow chamber has been evacuated, bubble free filling of the hollow chamber with a high vapor pressure liquid is effected by:
1. cooling the body of the implantable transducer to establish a temperature gradient therealong at least a portion of which has a temperature that is below a dew point of the high vapor pressure liquid; while concurrently
2. introducing into the entrance of the passage a vapor of the liquid.
Thus, upon condensation of the vapor within the hollow chamber of the implantable transducer, the hollow chamber becomes filled with the liquid without creating a bubble within the hollow chamber.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.